Catheter balloon mold form and molding process

ABSTRACT

An immersion mold for a medical device balloon. The mold has a cavity adapted to receive a hollow parison expandable therein to form the balloon. The cavity has a length, a first end, a second end, and a cavity wall with inner and outer surfaces. The mold form cavity wall is provided with one or a plurality of through-holes along the length thereof to facilitate entrance and egress of a heated fluid.

FIELD OF THE INVENTION

This invention pertains to a mold apparatus for forming medical deviceparts such as balloons employed on catheters, endoscopes and the like.

BACKGROUND OF THE INVENTION

U.S. Pat. No. 4,490,421 Levy, and U.S. Pat. No. 5,264,260, Saab,describe PET balloons. U.S. Pat. No. 4,906,244, Pinchuk et al, and U.S.Pat. No. 5,328,468, Kaneko, describe polyamide balloons. U.S. Pat. No.4,950,239, Gahara, and U.S. Pat. No. 5,500,180, Anderson et al describeballoons made from polyurethane block copolymers. U.S. Pat. No.5,556,383, Wang et al, and U.S. Pat. No. 6,146,356, Wang et al, describeballoons made from polyether-block-amide copolymers andpolyester-block-ether copolymers. U.S. Pat. No. 6,270,522, Simhambhatla,et al, describes balloons made from polyester-block-ether copolymers ofhigh flexural modulus. U.S. Pat. No. 5,344,400, Kaneko, describesballoons made from polyarylene sulfide. U.S. Pat. No. 5,833,657,Reinhart et al, describes balloons having a layer ofpolyetheretherketone. All of these balloons are produced from extrudedtubing of the polymeric material by a blow-forming radial expansionprocess.

A typical method for forming medical device balloons includes moldingthe balloon from a hollow parison, for instance an extruded tubularparison. The mold form for such processes is adapted to receive theparison of thermoplastic material and has a cavity into or through whichthe parison extends. Heat is applied to the mold, for instance byimmersion in a heated fluid, to soften the thermoplastic material.Concurrently, or in some sequence of heating and pressurization, theparison is pressurized to radially expand the softened thermoplasticmaterial until it contacts and conforms to the shape of the cavity. Thistypical method may be practiced in a variety of known ways, for instancewith or without an axial stretch step, which may be performed concurrentwith or prior to radial expansion and at temperature above or below aglass transition temperature. The parison may be expanded in severalsteps, each of which may be accompanied by a prior or concurrent axialstretching step. A heat setting step or an annealing step may beperformed after the balloon has been molded.

Mold forms for medical device balloons are typically provided with ahighly polished or glassy cavity surface which is unbroken, at leastover the body surface. In some cases, however a simple heated tube oflarger diameter than the parison is used, so that the balloon end conesare free-formed. In a further alternative a balloon may be free-blown ina heated media with cone end forms used to confine the balloon ends.

High strength medical device balloons formed in the manner used for suchapplications as angioplasty and stent placement in cardiovascularvessels are well known. Typically such balloons are designed to providea nominal inflated diameter of 6 mm or less. Recently, applications foreven larger balloons of similar high strength have been identified.

WO 98/03218 describes techniques for preparing large diameter balloons(5-30 mm dia.), using tubular parisons formed of certain block copolymermaterials and incorporating an annealing technique to widen the range ofdiameters obtainable over the range of useful inflation pressures. Theballoons of WO 98/03218 are useful in gastrointestinal surgicalprocedures.

As balloon size increases, the increasing distance between the walls ofthe mold and the parison within the mold can cause a higher variabilityin the balloons obtained, possibly due to increased variability in thelocation of initiation. The ability to control the initiation locationis typically difficult and delicate, as control of initiation requirescontrol of the temperature gradient location within the mold.Conventional fluid-heated immersion molding devices do not allow forrepeatable, accurate control of molding initiation location. With largerdiameter balloons, this lack of control can negatively affect propertiesand yields. Balloon properties which may be negatively affected includewall thickness uniformity, position of key transitions associated withcone wall mass removal, and ultimately balloon performance, ability tobe delivered, and overall balloon consistency. Therefore a need remainsfor improvements in balloon blowing processes, particularly for largediameter balloons.

SUMMARY OF THE INVENTION

The present invention is directed to a novel mold design for preparingmedical device balloons to a balloon blowing process, and to balloonsprepared by the process.

In one aspect the invention is directed to an immersion mold for amedical device balloon, the mold having a cavity adapted to receive ahollow parison expandable therein to form the balloon, wherein the moldform cavity wall is provided with at least one through-hole along thelength thereof to facilitate entrance and egress of a heated fluid.

In another aspect the invention is directed to a method of forming amedical device comprising the steps of

-   -   placing a parison in a mold having a cavity with a wall form        substantially conforming to the desired shape of said device,    -   immersing the mold in a heated liquid fluid to heat the parison,        and    -   pressurizing the parison to radially expand the parison to        contact the walls of the mold cavity, wherein:

the mold cavity wall contains at least one through-hole therein throughwhich the heated liquid fluid enters the mold cavity to directly contactthe parison when the mold is immersed in the heated fluid and throughwhich heated liquid fluid that has entered the mold cavity is expelledtherefrom when the parison is radially expanded.

In use, the heated fluid enters the mold cavity through thethrough-holes in the wall to directly contact the parison when the moldis immersed in the heated fluid. When the parison is radially expandedthe heated fluid that has entered the mold cavity is expelled from themold cavity via the same route.

Balloons formed using a mold form of the invention or according theprocess of the present invention constitute further aspects of theinvention. Still further aspects of the invention are described or arereadily apparent from the accompanying drawings, detailed descriptionand claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exterior side view, with partial cutaway, of a mold formaccording to one embodiment of the invention.

FIG. 2 is a sectional view taken along line 2-2 of FIG. 1.

FIG. 3 is an exterior side view of a mold form according to a secondembodiment of the invention.

FIG. 4 is a sectional view taken along line 4-4 of FIG. 3.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

All published documents, including all US patent documents, mentionedanywhere in this application are hereby expressly incorporated herein byreference in their entirety. Any copending patent applications,mentioned anywhere in this application are also hereby expresslyincorporated herein by reference in their entirety.

Referring to FIGS. 1 and 2, there is shown an immersion mold form 10according to one embodiment of the invention. Mold 10 has generallytubular end regions 11, 12, cone regions 13, 14 and a body region 16. Atleast one of the end regions 11, 12 is open to allow insertion of aparison. Typically the parison will be an extruded polymeric tube memberwhich is designed to be extended through both end regions. The mold form10 is adapted to be heated by immersion in a heated fluid media.

In accordance with the specific embodiment of the invention depicted inFIGS. 1-2, the interior cavity 18 of mold form 10 conforms generally tothe exterior shape of the mold. Thus, the end region 12 has acorresponding interior surface 20, of substantially constant diameter;the cone region 14 has a corresponding inner surface 21 which slopesoutwardly to a larger diameter at its junction with the cylindricalinner surface 22; and, inner surface 22, in turn, has the generallycylindrical shape of the exterior of the mold in the body region 16. Itshould be noted, however, that the balloon form is defined by the innersurfaces of the mold form cavity 18, not the exterior configuration.Consequently, it is not necessary that the outer surface correspond evenin a general way to the shape of the inner surface. Moreover, morecomplex shapes especially in the body and/or cone regions may beemployed. See for instance U.S. Pat. No. 6,290,485.

The mold form may be configured to open or disassemble, to facilitateremoval of the formed balloon. For a mold design as depicted in FIGS.1-2 a segmented configuration, for instance as depicted in the cut-awayportion of FIG. 1 or as depicted in FIG. 4 of U.S. Pat. No. 6,328,710,may be employed. Clam shell opening mechanisms, or other mold designswhich mate two longitudinal sections, may also be employed in designingmold forms of the invention

A characterizing feature of the inventive balloon molds is the presenceof at least one, preferably more than one, through-hole that extendsthrough the wall of the mold and opens into the inner cavity. In FIGS. 1and 2 these through-holes are depicted at 24 and are disposedlongitudinally relative to the central axis of the mold form, and spacedevenly around the circumference. Other patterns, however, are practicaland can be readily implemented without departing from the invention. Thelocation may be anywhere in the body, cone, and/or waist portions of themold. The through-holes provide means for the heating media, typicallyheated water or oil, to enter the mold as the parison is dipped from oneend down into a bath of the heating media. In this way heat istransferred much more directly to the parison.

The through-holes desirably will be of sufficiently large size that areproducibly more rapid thermal transfer is obtained as fluid flows inand out of the mold. On the other hand the through-hole dimensionsshould ordinarily not be so large that the parison materialsubstantially intrudes into the holes as it is brought into contact withthe chamber walls. Intrusion of parison material into the through-holescan provide the molded balloon with creases or dimples, which may beundesirable in some balloons. In many cases, however, minor crease ordimple patterns which may be expected in balloons formed in theinventive mold forms are usually acceptable. For at least some types ofballoons crease or dimple patterns may even be desirable, for instance,to facilitate refolding of the balloon after inflation or to providemounting sites for blade assemblies of a cutting balloon. In general,for rectangles and other holes having major and minor dimensions, theminor dimension of the through-holes may be from about 0.1 mm to about1.5 mm, for instance from about 0.2 to about 0.5 mm and the majordimension may be from about 0.2 mm to the full length or circumferenceof the mold form subject, the latter case of course being subject to theprovision of a mechanism for holding and maintaining the mold inassembled form. Exemplary such major dimensions include for instance0.5-10 cm. Suitable diameters for circular holes may be for instancefrom 0.1 mm to about 1.5 mm, for instance about 0.2 to about 0.7 mm.

The rapidity of the thermal transfer can be further facilitated byagitation of the fluid and/or molding apparatus vibration, for instanceby ultrasonic vibration.

The location of the through-holes may be such that, for a given dippingprocess, the heated fluid has had an opportunity to enter the chamberand contact the parison to the depth of dipping by the time thatinitiation of blowing is desired. Also suitably, the through-holes maybe spaced along the length of the mold so that heating media enteringthe mold is readily displaced out the same holes as the parison expandsto fill the chamber. In the embodiments of the Figures, longitudinallyoriented slots are provided with parallel sides and rounded ends.Alternative arrangements are feasible, including helical andcircumferential orientations. The longitudinal positions of slotthrough-holes may be staggered around the circumference so that at everylocation along the length of the body portion of the mold form at leastone opening exists somewhere on the circumference.

Preferably at least two openings exist along the body length tofacilitate both entrance of the heated fluid into the mold cavity andegress therefrom. In some cases it may be feasible to expel the fluidthough one or both ends of the mold cavity.

In one embodiment, a titanium mold form for a balloon having a bodycavity of about 8 mm diameter and 4 cm body length, was provided with aseries of 4 longitudinally extending slot columns spaced equally aroundthe circumference (i.e. at 90° intervals as shown in FIG. 2). Adjacentcolumns of slots were staggered with the number of slots alternatingbetween three and four slots/column, moving around the circumference ofthe mold. Each slot had a width of approximately 0.5 mm and a length ofapproximately 6 mm. The mold could be used to prepare balloons ofacceptable strength for angioplasty, gastrointestinal and/or stentplacement applications.

Although longitudinally oriented slot holes are shown in the Figures, itshould be understood that the through-holes can take virtually any shapeand need not be longitudinally oriented. The holes may be circular,rectangular, diamond, square oval, or any other shape feasible formanufacture. Helical through-hole orientation should also normally beacceptable. In some cases longitudinally spaced slot holes whose longdimension is oriented circumferentially, rather than longitudinally, mayalso be effective.

FIGS. 3 and 4 depict another embodiment of the invention. Mold form 30is substantially the same as mold form 10, except that the through-holes32 have a chamfer 34 which flares outwardly from the opening at thesurface of the inner cavity 36 to the outer surface of the mold. Thisdesign reduces the flow resistance of the heated media through the sideholes to some extent, without enlargement of the through-hole profile atthe mold cavity wall.

Mold forms of the invention may be made of any suitable material,preferably one which provides for a highly polished or glassy cavitysurface. Metal, such as titanium or stainless steel, are exemplarymaterials. Glass and ceramic materials may also be employed. Compositeand laminate materials are also suitable. Preferred are materials whichhave high heat conductivity, especially metals such as stainless steel,titanium, aluminum and the like.

The balloons are blown in the inventive molds using conventionalprocedures for immersion blow molding of catheter balloons. Such aprocess may include the steps of placing a parison in a mold having acavity with a wall form substantially conforming to the desired shape ofsaid device, immersing the mold in a heated fluid to heat the parison,and pressurizing the parison to radially expand the parison to contactthe walls of the mold cavity. The heated fluid enters the mold cavity todirectly contact the parison when the mold is immersed in the heatedfluid. As the parison softens and is pressurized it expands, expellingthe heated fluid that has entered the mold cavity therefrom andconforming itself to the mold cavity shape.

The heated fluid may be any fluid suited to the temperature of moldingand the materials of the mold form and the parison. Water at atemperature of about 90° C. to about 99° C. is exemplary. Other fluidssuch as glycerol, mineral oil or silicone oil at the same or highertemperature are also known and can be employed in the invention. Betweenthe various known fluids, those with relatively lower viscosities arepreferred.

Any balloon material suited to molding may be employed in the inventivemethod. Balloon materials which may be advantageously employed in theinvention are well known. Any material which can be molded from aparison may be feasibly employed in the invention. Such materialsinclude polyesters such as PET, PEN and PBT, polyurethane blockcopolymers such as ISOPLAST 301, PELLETHANE 2363-75D, and othermaterials described in U.S. Pat. Nos. 4,950,239 or 5,500,180; polyamideblock copolymers such as PEBAX 6333, PEBAX 7033 and PEBAX 7233, andother materials described in U.S. Pat. No. 5,556,383; polyamides such asnylon 12, nylon 11, nylon 10, and other materials described in U.S. Pat.No. 4,906,244; polymer blend materials such as single or multiphaseblends of liquid crystal polymers in another polymer, such as describedin U.S. Pat. 6,242,063, U.S. Pat. No. 6,284,333 or U.S. Pat. No.6,596,219; and polyester elastomer balloons such as ARNITEL EM 740,HYTREL 8238, and other materials described in U.S. Pat. Nos. 5,556,383or 6,270,522.

Direct transfer of heat from the heated fluid to the parison is thoughtto be more efficient than indirect transfer through the space betweenthe mold cavity and the parison. Therefore the inventive mold forms arebelieved to facilitate a more consistent initiation point for blowingthe balloons. As a result, more consistent and higher performanceballoon components can be obtained in markedly improved yields. Withoutbeing bound thereto, it is believed that the invention obtains thesebenefits by improving thermal transfer of the hot fluid heat source tothe interior of a large mold cavity. This improved thermal transfer isobtained by hot fluid delivery through the small channel orifices(through-holes) in the mold cavity. The direct contact of hot fluid withthe parison is seen to provide a much more efficient transfer of thermalenergy to the parison, thereby producing the reduced variability inballoon properties. This benefit becomes increasingly noticeable asballoon mold diameters increase above 5 mm, for instance with molddiameters about 6 mm to about 50 mm, especially those with diameters ofabout 8 mm or above.

The above examples and disclosure are intended to be illustrative andnot exhaustive. These examples and description will suggest manyvariations and alternatives to one of ordinary skill in this art. Allthese alternatives and variations are intended to be included within thescope of the claims, where the term “comprising” means “including, butnot limited to.” Those familiar with the art may recognize otherequivalents to the specific embodiments described herein whichequivalents are also intended to be encompassed by the claims. Further,the particular features presented in the dependent claims can becombined with each other in other manners within the scope of theinvention such that the invention should be recognized as alsospecifically directed to other embodiments having any other possiblecombination of the features of the dependent claims. For instance, forpurposes of claim publication, any dependent claim which follows shouldbe taken as alternatively written in a multiple dependent form from allclaims which possess all antecedents referenced in such dependent claimif such multiple dependent format is an accepted format within thejurisdiction. In jurisdictions where multiple dependent claim formatsare restricted, the following dependent claims should each be also takenas alternatively written in each singly dependent claim format whichcreates a dependency from an antecedent-possessing claim other than thespecific claim listed in such dependent claim.

1. A method of forming a medical device comprising the steps of placinga parison in a mold having a cavity with a wall form substantiallyconforming to the desired shape of said device, immersing the mold in aheated liquid fluid to heat the parison, and pressurizing the parison toradially expand the parison to contact the walls of the mold cavity,wherein the mold cavity wall contains at least one through-hole thereinthrough which the heated liquid fluid enters the mold cavity to directlycontact the parison when the mold is immersed in the heated fluid andthrough which heated liquid fluid that has entered the mold cavity isexpelled therefrom when the parison is radially expanded, the at leastone through-hole havin a first dimension of at least about 0.1 mm and asecond dimension of at least about 0.2 mm.
 2. The method of claim 1wherein the through-hole is formed as a slot.
 3. The method of claim 1wherein the through-holes are formed as longitudinally oriented slots.4. The method of claim 3 wherein the slots are arranged in a pluralityof circumferentially spaced columns.
 5. The method of claim 4 whereinthe slots of circumferentially alternating columns of slots arestaggered longitudinally.
 6. The method of claim 4 wherein the moldcavity wall has at least three of said circumferentially spaced columnsof slots.
 7. The method of claim 6 wherein the mold cavity wall has fourof said circumferentially spaced columns of slots.
 8. The method ofclaim 1 wherein the at least one through-hole has a dimension at themold cavity wall inner surface which does not allow substantialpenetration of the parison material therethrough when heated to thetemperature of the heated fluid and pressurized at a pressure sufficientto expand the parison to contact the mold cavity wall.
 9. The method ofclaim 1 wherein the at least one through-hole has a an oval, diamond orrectangular shape at the cavity wall inner surface.
 10. The method ofclaim 1 wherein the mold cavity wall has a plurality of saidthrough-holes arranged according to a pattern which extendscircumferentially around the cavity wall.
 11. The method of claim 1wherein the mold cavity wall has a plurality of said through-holesarranged according to a pattern which extends helically around thecavity wall.
 12. The method of claim 1 wherein the cavity has a portionhaving a diameter of at least 5 mm.
 13. The method of claim 12 whereinsaid diameter is from about 8 mm to about 50 mm.
 14. A method as inclaim 1, further comprising agitating the heated fluid while the mold isimmersed therein.
 15. A method as in claim 1 further comprisingvibrating the molding apparatus while the mold is immersed in the heatedfluid.
 16. A method as in claim 1 wherein the mold cavity wall containsa plurality of said through-holes therein.
 17. The method of claim 1wherein the heated liquid fluid is water, glycerol or an oil.
 18. Amethod of forming a medical device comprising the steps of placing aparison in a mold having a cavity with a wall form substantiallyconforming to the desired shape of said device, immersing the mold in aheated liquid fluid to heat the parison, and pressurizing the parison toradially expand the parison to contact the walls of the mold cavity,wherein the mold cavity wall contains at least one through-hole thereinthrough which the heated liquid fluid enters the mold cavity to directlycontact the parison when the mold is immersed in the heated fluid andthrough which heated liquid fluid that has entered the mold cavity isexpelled therefrom when the parison is radially expanded, the at leastone through-hole being substantially circular and having a diameter ofat least about 0.1 mm.